A prolog variant with guarded clauses and committed-choice nondeterminism (don't-care nondeterminism) by Ehud "Udi" Shapiro, Yale <shapiro-ehud@yale.edu>. A subset has been implemented, but not the full language.

See also mandala.

["Concurrent Prolog: Collected Papers", E. Shapiro, V.1-2, MIT Press 1987].